and a third supporting full marriage equality

I think you are being unfair here. Those against gay marriage also consider themselves to be in favor of full marriage equality; both straights and gays have equal right to marry anyone they like, so long as that person 1) consents 2) is unmarried 3) is of age 4) is of the opposite sex 5) etc. Indeed, if my sexual orientation flipped tomorrow, the set of people I could legally marry would not change at all.

This is not to say that this argument is correct. However, you are making a mistake by using the terminology to describe one side, in the same way that it would be unfair to describe the debate on obamacare as being between "those who want government healthcare, those who want some government intervention, and those who value individual rights"